1. Field of the Invention
The present invention relates to a method and apparatus for producing a formed structural element of fiber material bonded with synthetic resin such that a fine-grained or flowable synthetic resin bonding agent is sprinkled on or sprayed on a nonwoven fabric made entirely or predominantly of natural fibers. The nonwoven fabric which is permeated with synthetic bonding agent is fragmented, whereupon the parts are stored in a tower on a perforated female mold which belongs to a molding press and are precompressed on the female mold by means of an air stream that is suctioned through the perforations. To produce formed structural elements with a stable shape, the synthetic resin bonding agent, after a similarly perforated male mold has been placed on top and pressed on, is hardened by means of a hot air stream that is conducted through the perforations in the male mold and the female mold.
2. Description of the Prior Art
A method of the type described above is known, for example, from the FR-patent specification 76-20950 (publication No. 2 357 675). This method makes it possible to produce structural elements which exhibit a good cushioning effect, sound absorption, and heat insulation, and which therefore are used preferably for the inside lining of vehicle compartments. The method also makes it possible to produce structural elements with a prescribed outline and in this fashion to avoid material losses caused by cutting to size, losses which, for the above-mentioned application, according to experience amount to about 30% on the average.
A disadvantage of this known method is that sound absorption, which is especially important for the described application as an inside lining of vehicle compartments, practically cannot be optimized. It is possible for the parts or fibers of the nonwoven fabric and the fine-grained synthetic resin bonding agent to separate when they are stored in the tower, so that the stored parts of the nonwoven fabric or fibers contain different amounts of synthetic resin bonding agent depending on their location. When the synthetic resin bonding agent is hardened, this leads to areas with different bonding between the parts of the nonwoven fabric and fibers. As a result, the elasticity and the sound absorption depending on it will differ depending on location. With the known methods, a deposit necessarily has a thickness that is practically constant over its entire surface. If structural elements with a relief-like shape are produced from such a deposit, with a thickness that varies according to location, then the deposit must be compared to a different degree in correspondence with the location. This variably strong compaction creates regions with a different material density, which again leads to regions with different elastic modulus and thus also different sound absorption.